DE 10 2004 012 946 A1 discloses a wind turbine having a device for continuously discharging electrostatic energy between the rotor shaft and the machine frame of the nacelle. Here on the rotor shaft, a ring electrode is arranged, which produces a permanent electric connection between the rotor shaft and the ground in conjunction with a sliding contact device. Therefore, no charging of the rotor of the wind turbine can take place. Furthermore, in addition to the sliding contact device, an electrode is provided on the machine frame, which forms a spark gap together with the ring electrode. With the help thereof, the high-energy lightning current can be transmitted from the rotor shaft into the machine frame.
This design has following serious disadvantage that the lightning current transmission does not function reliably, and thus the aforementioned components are still exposed to a risk of damage. The reason for this lies in that the relative position of the rotor shaft with respect to the machine frame varies during operation, caused by the tolerance of the bearings and/or deformation of the shaft due to load changes. This results in that the sparking distance S of the spark gap varies significantly, sometimes up to five millimeters. If the spark gap is too large, then a lightning current would choose a path with least resistance, e.g., through the rotor bearings. It is also conceivable that the electrode touches the ring electrode, which can result in wearing or welding during a lightning current flow.